Method of forming metallic carbide based wear resistant coating on a combustion turbine component

ABSTRACT

A method of forming a wear resistant coating on a combustion turbine component includes melting an ingot including at least one metallic carbide to form a metallic liquid including at least one metallic carbide. The metallic liquid including at least one metallic carbide is atomized in an atmosphere to form a metallic powder including at least one metallic carbide. The metallic powder including at least one metallic carbide is milled to form a nanosized metallic powder including at least one metallic carbide. The nanosized metallic powder including at least one metallic carbide is thermally sprayed onto the combustion turbine component.

FIELD OF THE INVENTION

The present invention relates to the field of wear resistant coatings, and, more particularly, to metallic carbide based wear resistant coatings and associated methods.

BACKGROUND OF THE INVENTION

Components of combustion turbines are routinely subjected to harsh environments that include rigorous mechanical loading conditions from room temperature to high temperatures. For example, a compressor section and turbine section component such as a diaphragm, airfoil, compressor blade roots, compressor vane, casing, and blade ring experiences vibrations and dynamic forces that cause undesirable wear. Such a component can be provided with wear resistant coatings to reduce maintenance intervals and increase the life of the component.

One particular component that may be provided with a wear resistant coating is a combustor basket spring clip. Combustion baskets may experience premature material loss on spring clips thereof. The reason for material loss has been identified as fretting/adhesive wear. The combustion baskets show wear on the spring clips before their designed service lifetime has elapsed.

Severe wear may cause combustion basket spring clip failure and costly repair costs associated therewith. It is therefore desirable to extend the service interval of these combustor basket spring clips. One way to mitigate this fretting wear is through the application of such wear resistant coatings.

One method of applying a wear resistant coating to a substrate is known as thermal spraying. Thermal spraying is a continuous process wherein material is melted and accelerated to high velocities to impinge on a substrate, where it rapidly solidifies to form a thin “splat.” The melting and acceleration of the molten particles is typically provided by a combustion flame or thermal plasma.

Some efforts at providing effective wear resistant coatings have focused on the use of metal matrix composites. Metal matrix composites are typically made by dispersing a reinforcing material into a metal matrix. The metal matrix is a monolithic material into which the reinforcing material is embedded, and is continuous. A conventional method of dispersing the reinforcing material into the metal matrix is to form a powder of the reinforcing material and add the powder to a metallic liquid at a temperature lower than the melting point of the reinforcing material. The metallic liquid is then rapidly solidified by quenching. The results of the solidification are then crushed, milled, and deposited on a metal substrate to form a wear resistant coating thereon.

Other efforts at providing effective wear resistant coatings have instead focused on the use of cermets, which are composites of ceramics and metals. Some cermets may also be metal matrix composites, although cermets are typically less than 20% metal by volume.

U.S. Pat. Pub. No. 200710243335 to Belashchenko, for example, discloses a method of creating a wear resistant coating made from a metal and ceramic composite. A ceramic powder is dispersed within a metallic liquid. The dispersion is then atomized to form an amorphous metallic powder. This amorphous metallic powder is then deposited, using conventional deposition techniques, on a metal substrate to create the wear resistant coating.

U.S. Pat. No. 6,641,917 to Itsukaichi et al. discloses a cermet powder to be used for depositing a wear resistant coating on a metallic substrate. Tungsten carbide powder, chromium carbide powder, and nickel powder, together with a binder, are mixed into a solvent to form a slurry. The slurry is formed into a spherical agglomerated powder by means of a spray drier. The spherical agglomerated powder is subjected to de-waxing and sintering to remove the organic binder from the spherical agglomerated powder. After sintering, the spherical agglomerated is milled and then sprayed using conventional methods onto a metallic substrate.

U.S. Pat. No. 6,562,480 discloses a wear resistant coating for protecting surfaces undergoing sliding contact, such as piston rings in an internal combustion engine. A base metal powder, a hard ceramic component, and molybdenum powder are mixed in a dry state using a v-cone blender. The mixed powder is then deposited onto a piston ring substrate by high velocity oxygen-fuel deposition.

As combustion turbine efficiency increases, the components thereof are subjected to higher temperatures and more hostile operation conditions. Therefore, better wear resistant coatings and methods of forming wear resistant coatings are desirable.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of the present invention to provide a method for forming an enhanced wear resistant coating.

This and other objects, features, and advantages in accordance with the present invention are provided by a method of forming a wear resistant coating on a combustion turbine component comprising melting an ingot comprising at least one metallic carbide to form a metallic liquid comprising at least one metallic carbide. Additionally, the metallic liquid comprising at least one metallic carbide may be atomized in an atmosphere to form a metallic powder comprising at least one metallic carbide. Furthermore, the metallic powder comprising at least one metallic carbide may be milled to form a nanosized metallic powder comprising at least one metallic carbide. Moreover, the nanosized metallic powder comprising at least one metallic carbide may be thermally sprayed onto the combustion turbine component.

The nanosized metallic powder comprising at least one metallic carbide may be blended with at least one of carbon nanotubes and silver prior to thermal spraying. In addition, the atomization may comprise atomization by vapor phase deposition. Also, the nanosized metallic powder comprising at least one metallic carbide may be agglomerated prior to thermal spraying.

The at least one metallic carbide may comprise tungsten carbide. Tungsten carbide is an exemplary material from which to form a wear resistant coating because it is four times harder than titanium, twice as hard as steel, and is highly scratch resistant. The at least one metallic carbide may additionally or alternatively comprise chromium carbide. Chromium carbide is another exemplary material from which to form a wear resistant coating because it is highly resistant to corrosion and oxidation. The ingot may further comprise at least one of cobalt, chromium, and nickel.

The metallic liquid may be atomized in an inert atmosphere. Alternatively, the metallic liquid may be atomized in an oxidizing atmosphere. Atomizing the metallic liquid in an oxidizing atmosphere may facilitate the formation of in-situ oxide shells that may enhance certain properties of the metallic liquid.

Milling the metallic powder may include cryomilling or ball milling. Milling the metallic powder may also include jet milling. The thermal spraying may comprise at least one of thermal combustion spraying, thermal plasma spraying, air plasma spraying, and high velocity oxygen fuel spraying.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a method in accordance with the present invention.

FIG. 2 is a flowchart of an alternative embodiment of a method in accordance with the present invention.

FIG. 3 is a flowchart of yet another embodiment of a method in accordance with the present invention.

FIG. 4 is a front perspective view of a turbine blade having a wear resistant coating formed thereon in accordance with a method of the present invention.

FIG. 5 is a greatly enlarged cross sectional view of the turbine blade taken along line 5-5 of FIG. 4.

FIG. 6 is a front perspective view of combustion basket spring clip indicating wear areas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Referring initially to FIG. 1, a first embodiment of a method of forming a wear resistant coating on a combustion turbine component in accordance with the present invention is now described generally with reference to the flowchart 10 of FIG. 1. After the start (Block 12), at Block 14, an ingot comprising at least one metallic carbide is melted to form a metallic liquid comprising at least one metallic carbide. An exemplary starting ingot comprises tungsten carbide or chromium carbide. Tungsten carbide is extremely hard and highly scratch resistant while chromium carbide is highly resistant to both corrosion and oxidation. Various processes may be utilized to melt the ingot, as will be appreciated by those of skill in the art.

At Block 16, the metallic liquid comprising at least one metallic carbide is atomized in an atmosphere to form a metallic powder comprising at least one metallic carbide.

At Block 18, the metallic powder comprising at least one metallic carbide is milled to form a nanosized metallic powder comprising at least one metallic carbide. The metallic powder comprising at least one metallic carbide may be milled for a desired length of time and according to one or more conventional milling processes as understood by those skilled in the art. Furthermore, the metallic powder comprising at least one metallic carbide may be milled multiple times by the same milling process, or may alternatively be milled multiple times by different milling processes. The at least one metallic carbide may comprise chromium carbide, for example.

At Block 20, the nanosized metallic powder comprising at least one metallic carbide is thermally sprayed onto the combustion turbine component. It is to be understood that any of a number of commercially available thermal spraying process may be employed, melting the nanosized metallic powder and accelerating it at the combustion turbine component. The nanosize of the metallic powder may advantageously allow for a finer splat structure that results in a more dense wear resistant coating. This greater density may facilitate superior properties, such as decreased porosity, greater hardness, greater creep resistance, and enhanced wear resistance. The nanosized particles causes smaller debris that creates a lubricious layer and also reduced abrasive wear.

Referring now to the flowchart 30 of FIG. 2, an alternative embodiment of the method of forming a wear resistant coating on a combustion turbine component is now described. After the start (Block 32), at Block 34, an ingot comprising tungsten carbide and cobalt is melted to form a metallic liquid comprising tungsten carbide and cobalt. It should be appreciated that, in other embodiments, the metallic liquid may comprise chromium carbide, nickel, and chrome. Indeed, the metallic liquid may comprise a variety of carbides and a variety of metals, as will be appreciated by those of skill in the art.

At Block 36, the metallic liquid comprising tungsten carbide and cobalt is atomized in an atmosphere to form a metallic powder comprising tungsten carbide and cobalt.

It will be appreciated by those of skill in the art that the atmosphere may be an oxidizing atmosphere, at a desired temperature, and at a desired pressure. Atomizing the metallic liquid in an oxidizing atmosphere may facilitate the formation of in-situ oxide shells that may enhance certain properties of the metallic liquid.

In some embodiments, the atmosphere may instead be an inert atmosphere, preferably comprising nitrogen and/or argon, although it is to be understood that other inert atmospheres, or even a vacuum, may be used. Atomization in such an inert atmosphere may increase the likelihood that each droplet or particle formed during the atomization process has a uniform size, shape, and/or chemistry.

At Block 38, the metallic powder comprising tungsten carbide and cobalt is cryomilled, ball milled, and/or jet milled to form a nanosized metallic powder comprising tungsten carbide and cobalt.

At Block 40, the nanosized metallic powder comprising tungsten carbide and cobalt is blended with carbon nanotubes and/or silver to enhance the wear resistance of the wear resistant coating. This blending, however, may lower the coefficient of friction of the wear resistant coating.

At Block 42, the nanosized metallic powder comprising tungsten carbide and cobalt is thermally sprayed onto the combustion turbine component. The resulting wear resistant coating comprises hard tungsten carbide particles in a soft cobalt matrix and may be considered to be a cermet. If the metallic liquid at Block 34 had included chromium carbide, nickel, and chromium, the resulting wear resistant coating would instead comprise hard chromium carbide in a soft nickel-chrome matrix, as will be understood by those skilled in the art.

Referring now to the flowchart 50 of FIG. 3, yet another embodiment of the method of forming a wear resistant coating on a combustion turbine component is now described. After the start (Block 52), at Block 54 an ingot comprising chromium carbide, nickel, and chromium is melted to form a metallic liquid comprising chromium carbide, nickel, and chromium.

At Block 56, the metallic liquid comprising chromium carbide, nickel, and chromium is atomized by vapor phase deposition in an atmosphere to form a metallic powder comprising chromium carbide, nickel, and chromium. At Block 58, the metallic powder comprising chromium carbide, nickel, and chromium is milled to form a nanosized metallic powder comprising chromium carbide, nickel, and chromium.

At Block 60, the nanosized metallic powder comprising chromium carbide, nickel, and chromium is agglomerated. The agglomeration produces micron sized particles which may be advantageous for use with some types of thermal spraying, for example High Velocity Oxygen Fuel Spraying (HVOF).

The agglomeration is performed by dispersing the nanosized metallic powder in a polar or non-polar solvent into which a suitable plasticizer, binder, and dispersant have been added, thereby forming a colloid. A variety of plasticizers, binders, and dispersants may also be used, as will be appreciated by those of skill in the art. The charge around the particles of the powder may be controlled with charge controlling agents (CCA's) or by altering the pH of the solvent, thereby changing the zeta potential of the system. This allows selective control of the size of the agglomerated particles, as the zeta potential of the system directly affects the size of the agglomerated particles. The agglomerated particles may then be removed from the colloid by conventional processes known to those of skill in the art.

At Block 62, the agglomerated metallic powder comprising chromium carbide, nickel, and chromium is thermally sprayed onto the combustion turbine component via thermal combustion spraying, thermal plasma spraying, air plasma spraying, or high velocity oxygen fuel spraying. The resulting wear resistant coating comprises hard chromium carbide particles in a soft nickel-cobalt matrix.

Referring now additionally to FIGS. 4-5, a turbine blade 70 having a wear resistant coating 74 formed in accordance with the method of the present invention is now described. The turbine blade 70 comprises a metal substrate 72. The wear resistant coating 74, as described above, is formed on the metal substrate.

It will be readily understood by those of skill in the art that the wear resistant coating 74 discussed above could be formed on any combustion turbine component such as diaphragm hooks, root of the blade, compressor vane roots, casing grooves, or blade ring grooves. The wear resistant coating methods described herein may also be used on other workpieces as will be appreciated by those skilled in the art.

One advantageous application for the wear resistant coatings disclosed herein is a combustor basket spring clip 75, as shown in FIG. 6.

As explained earlier, combustion baskets may experience premature material loss on spring clips thereof. The reason for material loss has been identified as fretting wear. Fretting wear is the repeated cyclical rubbing between two surfaces, which is known as fretting, over a period of time which will remove material from one or both surfaces in contact. Combustion basket spring clips 75 have been found to experience an excessive amount of such wear at a wear portion 76 thereof before their designated service lifetime has elapsed.

Severe wear may cause failure of the combustion basket spring clip 75 and costly repairs associated therewith. It is therefore desirable to extend the service interval of these combustor basket spring clips 75. Application of the wear resistant coatings described herein may help mitigate fretting wear at the wear portion 76, advantageously extending the service interval of the combustor basket spring clip 75.

Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims. 

1. A method of forming a wear resistant coating on a combustion turbine component comprising: melting an ingot comprising at least one metallic carbide to form a metallic liquid comprising at least one metallic carbide; atomizing the metallic liquid comprising at least one metallic carbide in an atmosphere to form a metallic powder comprising at least one metallic carbide; milling the metallic powder comprising at least one metallic carbide to form a nanosized metallic powder comprising at least one metallic carbide; and thermal spraying the nanosized metallic powder comprising at least one metallic carbide onto the combustion turbine component.
 2. A method according to claim 1 further comprising blending the nanosized metallic powder comprising at least one metallic carbide with at least one of carbon nanotubes and silver prior to thermal spraying.
 3. A method according to claim 1 wherein atomizing comprises atomizing by vapor phase deposition; and further comprising agglomerating the nanosized metallic powder comprising at least one metallic carbide prior to thermal spraying.
 4. A method according to claim 1 wherein the at least one metallic carbide comprises tungsten carbide.
 5. A method according to claim 1 wherein the at least one metallic carbide comprises chromium carbide.
 6. A method according to claim 1 wherein the ingot further comprises at least one of cobalt, chromium, and nickel.
 7. A method according to claim 1 wherein the atmosphere comprises an inert atmosphere.
 8. A method according to claim 1 wherein the atmosphere comprises an oxidizing atmosphere.
 9. A method according to claim 1 wherein milling the metallic powder comprises at least one of cryomilling, ball milling, and jet milling.
 10. A method according to claim 1 wherein thermal spraying comprises at least one of thermal combustion spraying, thermal plasma spraying, air plasma spraying, and high velocity oxygen fuel spraying.
 11. A method of forming a wear resistant coating on a combustion turbine component comprising: melting an ingot comprising tungsten carbide and cobalt to form a metallic liquid comprising tungsten carbide and cobalt; atomizing the metallic liquid comprising tungsten carbide and cobalt in an inert atmosphere to form a metallic powder comprising tungsten carbide and cobalt; milling the metallic powder comprising tungsten carbide and cobalt to form a nanosized metallic powder comprising tungsten carbide and cobalt; and thermal spraying the nanosized metallic powder comprising tungsten carbide and cobalt onto the combustion turbine component.
 12. A method according to claim 11 further comprising blending the nanosized metallic powder comprising tungsten carbide and cobalt with at least one of carbon nanotubes and silver prior to thermal spraying.
 13. A method according to claim 11 wherein atomizing comprises atomizing by vapor phase deposition; and further comprising agglomerating the nanosized metallic powder comprising tungsten carbide and cobalt prior to thermal spraying.
 14. A method according to claim 11 wherein milling the metallic powder comprises at least one of cryomilling, ball milling, and jet milling.
 15. A method according to claim 11 wherein thermal spraying comprises at least one of thermal combustion spraying, thermal plasma spraying, air plasma spraying, and high velocity oxygen fuel spraying.
 16. A method of forming a wear resistant coating on a combustion turbine component comprising: melting an ingot comprising chromium carbide, nickel, and chromium to form a metallic liquid comprising chromium carbide, nickel, and chromium; atomizing the metallic liquid comprising chromium carbide, nickel, and chromium in an oxidizing atmosphere to form a metallic powder comprising chromium carbide, nickel, and chromium; milling the metallic powder comprising chromium carbide, nickel, and chromium to form a nanosized metallic powder comprising chromium carbide, nickel, and chromium; and thermal spraying the nanosized metallic powder comprising chromium carbide, nickel, and chromium onto the combustion turbine component.
 17. A method according to claim 16 further comprising blending the nanosized metallic powder comprising chromium carbide, nickel, and chromium with at least one of carbon nanotubes and silver prior to thermal spraying.
 18. A method according to claim 16 wherein atomizing comprises atomizing by vapor phase deposition; and further comprising agglomerating the nanosized metallic powder comprising chromium carbide, nickel, and chromium prior to thermal spraying.
 19. A method according to claim 16 wherein milling the metallic powder comprises at least one of cryomilling, ball milling and jet milling.
 20. A method according to claim 16 wherein thermal spraying comprises at least one of thermal combustion spraying, thermal plasma spraying, air plasma spraying, and high velocity oxygen fuel spraying. 